This page was produced using a tutorial from freeCodeCamp.
You can choose one of the three colours shown for this circle, or else using the 'random' button you can make it any colour you like - as long as you're patient.
The circle is actually a <div> element made circular by setting the border radius parameter to 50%.
Each button sends a text instruction to a simple script which then sets the colour of the <div> element to match.
If you choose random, code is executed to instead generate a hexadecimal value to use instead.